1. Field of the Invention
The present invention relates to a terminal structure employed in an inner rotor-type motor, and more particularly, to a terminal structure of a motor suitable for connection by welding.
2. Description of the Related Art
In recent years, from demands for environmental pollution-control measures, etc., solder for welding or attaching various kinds of parts is desired to be lead-free. Accordingly, research on lead-free solder (solder containing no lead) has been actively carried out. Use of lead-free solder also for connecting ends of a magnet wire of a motor coil is being considered.
For instance, in case of a PM-type stepping motor, after a an end part of a magnet wire from a coil is bound several turns around a terminal press-fitted into a terminal block (bobbin), the terminal is dipped in a solder bath filled with molten solder to detach an insulation coating from the magnet wire and at the same time to connect a copper lead wire as a core wire and the terminal by means of soldering, wherein the above mentioned lead-free solder is expected to be used.
However, though the lead-free solder is expected to be used in the connection of the end of magnet wire of the PM-type stepping motor, the molten lead-free solder suffers an intense oxidization and becomes brittle (so-called cold solder) unless placed ina reduced atmosphere of nitrogen. Thus, its reliability cannot be ensured and the lead-free solder has not been adopted.
The lead-free solder, from the view point of its characteristics, is subject to various restrictions such as a method of use and its solderability with objects to be soldered, and further, compared with a conventional eutectic-type solder, has a higher melting point, is more liable to cause a problem like a poor contact, requires a higher level of soldering technique, is more difficult to use, and is more expensive as well. So, an alternative to the lead-free solder has been under consideration.
The present invention has been made in view of the above-mentioned circumstances, and therefore has an object to provide a motor terminal having a structure which enables a coil and an external circuit to be connected securely and with a good workability, while saving material resources and increasing safety relating to environmental pollution.
According to a first aspect of the present invention, there is provided a terminal structure for a motor which comprises a stator in which-a coil formed by winding a magnet wire around a bobbin made of an insulating material is inserted in a stator yoke made of a soft magnetic material and a rotor which includes a permanent magnet rotatably arranged in an inner circumference of the stator, the terminal structure characterized in that the bobbin includes a terminal for connecting the coil and an external circuit and that the terminal consists integrally of a magnet wire binding section to connect to the magnet wire of the coil, an external connection section to connect to the external circuit and a support base section to press-fit into a terminal block (bobbin) and hold the terminal onto the block.
That is, in the first aspect of the present invention, the terminal is structured into three sections by function. The first is the magnet wire binding section that does a function of a terminal to connect to the magnet wire from the coil wound around the bobbin, the second is the external connection section that has a function of a terminal to connect to the external circuit, and the third is the support base section that press-fits into the terminal block and hold the terminal onto the block. While these three sections are adapted to be handled independently of each other, they are structured integrally so as to be handled as a single terminal.
The reason for employing the structure of the terminal composed of three sections is as follows. When connecting an end of magnet wire, that is, connecting, by means of fusing (plasma welding), the magnet wire bound around the magnet wire binding section to the terminal, a discharge current resulting from plasma welding must be allowed to flow, and therefore a ground electrode of a plasma welding machine is connected to the external connection section which is electrically continuous with a welded portion, thereby enabling the welding operation and also enabling the terminal to connect externally without getting melted or deformed by the welding.
Note that the terminal may be so structured that a direction and position of the terminal may be settled by press-fitting a junction of the magnet wire binding section, the external connection section and the support base section, together with the support base section, into a guide hole and a groove provided in the terminal block.
According to a second aspect of the present invention, in the terminal structure according to the first aspect of the present invention, at least one of a projection and a recess, for preventing the terminal from pulling out from the terminal block, is formed at the support base section.
According to a third aspect of the present invention, in the terminal structure according to the first or second aspect of the present invention, the length of the external connection section is greater than the length of the magnet wire binding section.
The reason the length of the external connection section is set greater than that of the magnet wire bending section is, to make the connection of the ground electrode easier when connecting the magnet wire from the coil onto the magnet wire binding section by plasma welding, and make the external connection of the terminal easier. The length of the external connection section may be set equivalent to the length of the magnet wire binding section.
According to a fourth aspect of the present invention, in the terminal structure according to any one of the first to third aspects of the present invention, the connection of the magnet wire binding section and the magnet wire of the coil is carried out by means of fusing.
According to a fifth aspect of the present invention, in the terminal structure according to any one of the first to third aspects of the present invention, the connection of the magnet wire binding section and the magnet wire of the coil is carried out by resistance welding.
According to a sixth aspect of the present invention, in the terminal structure according to any one of the first to fifth aspects of the present invention, the support base section and the external connection section are both formed in a rectangular shape and connected to each other in series longitudinally, the magnet wire binding section is formed in a substantially L-shape with a first wing thereof joining with the junction of the support base section and the external connection section in such a manner that the first wing is perpendicular to the support base section and that a second wing thereof is parallel with the external connection section with a given distance therebetween, and the length of the second wing is set different from that of the external connection section.
According to a seventh aspect of the present invention, in the terminal structure according to the sixth aspect of the present invention, an end portion of magnet wire of the coil is bound around the second wing of the magnet wire binding section and the length of the second wing is set so that the distance from an end of the binding of the magnet wire to a tip end of the second wing falls within a range of 0.5 to 3 mm.
According to an eighth aspect of the present invention, in the terminal structure according to any one of the first to fifth aspects of the present invention, the support base section and the external connection section are both formed in a rectangular shape and connected to each other in series longitudinally, the magnet wire binding section. is formed in a substantially L-shape with a first wing thereof joining with the conjunction of the support base section and the external connection section in such a manner that the first wing is perpendicular to the support base section and that a second wing thereof is parallel with the external connection section with a given distance therebetween, the length of the external connection section is set larger than the length of the second wing, and the junction of the support base section, the external connection section and the first wing of the magnet wire binding section, as well as the support base section, is adapted to press-fit into the terminal block (bobbin).
According to a ninth aspect of the present invention, in the terminal structure according to the eighth aspect of the present invention, the tip end of magnet wire of the coil is bound around the second wing of the magnet wire binding section, and the length of the second wing is set so that the distance from an end of the binding of the magnet wire to a tip end of the second wing falls within a range of 0.5 to 3 mm.
According to a tenth aspect of the present invention, in the terminal structure according to any one of the first to ninth aspects of the present invention, a lead terminal for bridging the external connection section and the external circuit is connected to the external connection section by resistance welding.
According to an eleventh aspect of the present invention, in the terminal structure according to the tenth aspect of the present invention, a groove into which the lead terminal fits is provided at the tip end of the external connection section.
According to a twelfth aspect of the present invention, in the terminal structure according to the tenth aspect of the present invention, the lead terminal is set wider at an end joining with the external connection section, and a groove is provided at the center of the wider portion for fixing the external connection section.